[PATCH v4 2/3] jump_label: Warn on failed jump_label patch

From: Josh Poimboeuf
Date: Tue Feb 20 2018 - 12:38:57 EST


When the jump label code encounters an address which isn't recognized by
kernel_text_address(), it just silently fails.

This can be dangerous because jump labels are used in a variety of
places, and are generally expected to work. Convert the silent failure
to a warning.

This won't warn about attempted writes to tracepoints in __init code
after initmem has been freed, as those are already guarded by the
entry->code check.

Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
---
kernel/jump_label.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index b71776576a66..b2f0b479191b 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -367,12 +367,15 @@ static void __jump_label_update(struct static_key *key,
{
for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) {
/*
- * entry->code set to 0 invalidates module init text sections
- * kernel_text_address() verifies we are not in core kernel
- * init code, see jump_label_invalidate_module_init().
+ * An entry->code of 0 indicates an entry which has been
+ * disabled because it was in an init text area.
*/
- if (entry->code && kernel_text_address(entry->code))
- arch_jump_label_transform(entry, jump_label_type(entry));
+ if (entry->code) {
+ if (kernel_text_address(entry->code))
+ arch_jump_label_transform(entry, jump_label_type(entry));
+ else
+ WARN_ONCE(1, "can't patch jump_label at %pS", (void *)entry->code);
+ }
}
}

--
2.14.3